Simplify the following expression: $n = \dfrac{r^2 + 17r + 72}{r + 8} $
Explanation: First factor the polynomial in the numerator. $ r^2 + 17r + 72 = (r + 8)(r + 9) $ So we can rewrite the expression as: $n = \dfrac{(r + 8)(r + 9)}{r + 8} $ We can divide the numerator and denominator by $(r + 8)$ on condition that $r \neq -8$ Therefore $n = r + 9; r \neq -8$